The present disclosure relates to a method for operating a battery system, to a battery system which can be operated in accordance with the method, and to a motor vehicle having the battery system.
Battery systems for use in motor vehicles, also called traction batteries, constitute, as is known, an interconnection of a plurality of individual battery cells or battery modules which comprise battery cells. Battery systems of this kind have a comparatively high battery capacity in comparison to consumer batteries. In order to be able to deliver a sufficient amount of power in every drive state of the motor vehicle, for example during start-up, battery systems of this kind are designed to be resistant to high currents. The rated voltage of the battery system is defined by series interconnection of battery cells or battery modules, and parallel connection of battery cells or battery modules is frequently additionally employed in order to increase the battery system capacity.
Conventional batteries have an inherent internal resistance. A voltage loss which reduces the voltage which is output by the battery is dropped across the internal resistance. If current is drawn from a battery, that is to say the battery is subjected to loading, the internal resistance of said battery changes dynamically in the meantime. If, for example, a lithium-ion battery is discharged with a current, for example 1 C at a battery capacity of 60 Ah, the profile for the output voltage of the lithium-ion battery which is shown in FIG. 1 is established. After a current jump, the voltage initially runs at a constant plateau and then drops since the internal resistance increases in the meantime.
DE 10 2010 041 014 also discloses a method for operating a battery system. The battery system has a battery which, for its part, has a battery module line with a plurality of battery modules which are connected in series. Each battery module comprises a coupling unit which is designed to decouple the battery module from the battery module line, to bridge the battery module or to connect the battery module to the other battery modules in series, so that a voltage across the battery module line can be variably adjusted, that is to say can be increased or lowered.